The objective is to elucidate the mechanism by which respiratory virus infections provoke attacks of asthma. Neutrophils will be incubated with culture supernates of rhinovirus and influenza viruses, and the effect of the virus preparations on the neutrophil response to the agonists isoproterenol, histamine and prostaglandin determined. The culture supernates will be subjected to various physical and chemical procedures to define the nature of the factor that impairs agonists response. Human tracheobronchial smooth muscle will be similarly incubated with these factors to assess their effect on agonist responses. Agonists responses of tracheas of guinea pigs infected with parainfluenza virus will be compared with responses of normal guinea pig trachea.